The tremor or involuntary quivering of your clutch foot (when you are driving stick ) and you just had a near-miss of an accident or you are being pulled off by a cop and you have drugs in your trunk or on your person. It is coursed by fear.

Druggie 1: Calm down man, you will get us busted

Driver druggie: I am calm!

Druggie 1: Oh yeah? then why is your leg bouncing up and down? You are scared man! you have clutch foot syndrome!